The present invention relates to a method and an apparatus for detecting the fluidity of powder.
In a copier or a printer, powdery toner is supplied to a latent image formed on a photoreceptor so that the latent image can be developed. Therefore, the powdery toner loaded in a developing unit is conveyed to the photoreceptor. In the case of toner to be mixed with a magnetic carrier, toner and carrier are stirred in the developing unit.
In this case, when the toner or the mixture (developer) of toner and carrier has a low fluidity, a sufficient amount of toner can not be supplied to the photoreceptor, or the toner can not be sufficiently mixed with carrier, so that the performance of development and transfer is lowered and the image quality is deteriorated, that is, unevenness of image density is caused. In order to solve the above problems, it is preferable to increase the fluidity of the developer or to improve the development and transfer function.
However, a detector to detect the fluidity of developer has not been provided yet. Therefore, the above problems can not be solved until now.
In general, when an angle of repose of powder is measured, the fluidity can be known. However, such a method takes a long period of time, and moreover it is impossible to apply the method to the measurement of powder put in a container.
In this connection, there is conventionally provided a detector to detect a residual amount of toner by oscillating longitudinal ultrasonic waves, however, this type of detector only detects the existence of residual toner, so that the fluidity of powder can not be detected with ultrasonic waves.
In view of the aforesaid conventional problems, the present invention has been achieved. The first object of the present invention is to provide a fluidity detection method and apparatus by which the fluidity of powder can be directly measured while the powder is put in a container.
Conventionally, an image forming apparatus has been known, in which: an electrostatic latent image is formed on a photoreceptor drum by an optical exposure system; the electrostatic latent image is developed with a developing unit using toner; the toner image is transferred onto a recording sheet; and the transferred toner image is fixed. This image forming apparatus is disclosed in Japanese Patent Application Open to Public Inspection Nos. 38482/1982 and 157070/1987.
Both one component and two component type developers are used for the above developing unit. The two component type developer is composed of magnetic carrier particles and nonmagnetic synthetic resin toner particles, wherein the magnetic carrier particles and nonmagnetic synthetic resin toner particles are mixed at an appropriate mixing ratio. Therefore, the toner particles mixed with the carrier particles are conveyed to a development sleeve of the developing unit, and deposited on an electrostatic latent image portion on the photoreceptor surface so that a toner image can be formed.
In the case where the two component type developer is used, only toner is consumed, and carrier is repeatedly circulated in the developing unit. Therefore, a toner concentration sensor to measure the concentration of toner is provided in the developing unit, and toner is appropriately replenished in accordance with the result of the detection, and the developer is stirred in the developing unit so that the developer can be appropriately charged and mixed at a predetermined mixing ratio.
In this connection, in the toner image formation described above, when the fluidity of developer (toner or a mixture of toner and carrier) is lowered, the adhesive force among the developer particles is increased. Accordingly, even when the substantial toner concentration is appropriate, the developed toner image becomes uneven and blurred, so that the image quality is deteriorated.
However, the conventional image forming apparatus are not provided with a sensor to detect the fluidity of developer. Therefore, the occurrence of defective images caused by the lowered fluidity can not be avoided.
In order to detect the fluidity of powder such as developer, there is provided a method by which an angle of repose of powder is measured. However, this method takes a long period of time, and moreover it is difficult to measure an angle of repose while the powder is put in a container. Therefore, it is substantially impossible to apply this method to an image forming apparatus so as to solve the problem of lowered fluidity.
In view of the aforesaid problems, the present invention has been achieved. The second object of the present invention is to provide an apparatus to which a sensor to quickly detect the fluidity of developer is provided so that the deterioration of image quality can be avoided in accordance with the result of detection of fluidity.
As a method to detect an amount of residual toner in a hopper, there is provided a method in which a microswitch is turned on and off in accordance with the weight of toner, and also there is provided a method in which an amount of residual toner is detected with an electrical means by measuring a dielectric constant of toner.
However, toner is essentially light, and the dielectric constant of toner is not large. Accordingly, the aforesaid residual toner amount detection methods can not provide sufficient sensitivity, stability and reliability.
In order to solve the above problems, the present inventors have proposed a method to detect an amount of residual toner characterized in that: an oscillating member is provided in a toner hopper or on a hopper wall surface; and an amount of toner deposited on the oscillating member is detected by an amount of displacement of the oscillating member, for example, the resonance frequency of the oscillating member. This method is disclosed in Japanese Patent Application Open to Public Inspection No. 36874/1980.
Specifically, the aforesaid oscillating member is a piezoelectric element oscillated in a thickness direction, that is, a piezoelectric element generating longitudinal waves, and the piezoelectric element is arranged so that the toner can be deposited on a surface of the piezoelectric element perpendicular to the oscillating direction. Therefore, an amount of residual toner can be detected when a difference is found between the oscillation characteristics.
However, by the aforesaid residual toner detection method, a toner amount is detected when a pressure of toner (weight of toner) impressed upon the piezoelectric element in an oscillating direction is measured. Accordingly, the following problems are caused: The detection characteristics are changed according to the type of toner and the condition of toner coagulation, so that the piezoelectric element must be selected each time the toner type is changed. Also, when the toner is coagulated due to moisture, it is impossible to ensure the stability of detection.
The present invention has been achieved while consideration is also given to the above problems. The third object of the present invention is to provide a residual toner amount detection apparatus by which the high detection stability can be ensured irrespective of the type of toner and the condition of toner coagulation.
Consideration is given to the problems described before, and in the present invention, powder is made to come into contact with a surface parallel with the oscillating direction of an oscillating element, and when a change in the electric characteristics of the oscillating element is measured, the condition of powder can be detected. In this case, the condition of powder is defined as the fluidity and residual amount.